k is dividing on the left, then it will multiply on the right
15 is dividing on the right, then it will multiply on the left
[tex]\begin{gathered} 3\cdot15=5\cdot k \\ 45=5\cdot k \end{gathered}[/tex]5 is multiplying on the right, then it will divide on the left
[tex]\begin{gathered} \frac{45}{5}=k \\ 9=k \end{gathered}[/tex]